Compact construction machines, for example skid steer loaders, are commonly used in applications where working space is limited. These machines include a frame that supports an internal combustion engine, and left and right undercarriages that transfer power from the engine to a ground surface. Typical compact construction machines utilize rigid mounting between the frame and the undercarriages, with sprockets of the undercarriages being indirectly driven by the engine via a hydraulic motor. This type of mounting between the frame and the undercarriages, because of its rigidity, can transfer machine-induced loads and vibrations to an operator, making long periods of machine usage uncomfortable for the operator. In addition, the rigid mounting can, in some instances, cause one of the undercarriages to lift off of the ground surface, thereby reducing traction, steering control, and machine stability.
Another type of suspension system for a compact construction machine is described in U.S. Patent Publication No. 2009/0321152 of Arulraj a et al. that was published on Dec. 31, 2009 (“the '152 publication”). Specifically, the '152 publication discloses a machine having a frame, a front torsion axle assembly, a rear torsion axle assembly, and a tracked undercarriage. The front and rear torsion axle assemblies each include a torsion arm, a torsion shaft, and an axle. The torsion shaft and the axle extend in different directions from opposing ends of the torsion arm. The torsion shafts of the front and rear torsion axle assemblies are rigidly attached to the frame at spaced apart fore and aft locations. The axle of the front torsion axle assembly is attached via a sleeve bearing to an upper frame surface of the undercarriage, while the axle of the rear torsion axle assembly is attached via a sleeve bearing located within the frame at a position just forward of a drive sprocket. The torsion arm of the front torsion axle assembly extends upward from the frame at an angle between 90 and 180 degrees. The torsion arm of the rear torsion axle assembly extends downward from the frame at an angle between 270 and 360 degrees.
During loaded operation of the machine of the '152 publication, the torsion axle assemblies are configured to flex independently. In particular, as the machine becomes loaded, because of a transverse offset between the torsion shaft and the axle of each assembly, a moment is created about each axle that causes individual torsion arms to rotate against a cushion of rubber cords located within the torsion shaft. This cushioned rotation causes the machine frame to move rearward and downward relative to the undercarriage, reducing a risk of tipping at both the front and rear torsion axle assemblies and increasing a reaction force at the front torsion axle assembly.